PDX mechanical divertor experiments

A preliminary plasma edge particle scoop limiter has been installed on the equator of the Princeton Divertor Experiment (PDX), a large tokamak. The scoop limiter is unique in that it is designed such that the plasma plugs the entrance throat thereby impeding the return flow of neutralized gas to the discharge. Neutral gas pressures of the order of 50 microns were measured inside the scoop. The pressure dependence on electron density in the scrapeoff plasma at the throat entrance was stronger than linear. A full size scoop limiter is under construction and will soon be installed on PDX. It has been designed to be sufficiently thermally robust so as to act as the sole limiter in a PDX discharge with 1.5 MW of neutral beam heating. (orig.)